1. Field of the Invention
The present invention relates to a method in the production of a magnetic head and more particularly to a method of annealing processing a magnetic head under a magnetic field.
2. Description of the Prior Art
There has been known to the public magnetic heads made using such a magnetic material that the magnetic anisotropy is induced under a magnetic field during an annealing process in at least a part of the magnetic head In the process of manufacturing the magnetic heads of the above type, there is generated a plurality of magnetic domains in the magnetic material, causing the permeability to be decreased due to generation of the magnetic anisotropy for stabilizing the magnetization in the magnetic domains and magnetic walls. In order to decrease the effect of the generation of the anisotropy, the magnetic material is usually subjected to an annealing process under a magnetic field. In the annealing process under the magnetic field, various experiments have been made to seek suitable processing conditions such as the magnetic directions and temperature and time of the annealing processing. Particularly, in order to manufacture the magnetic heads with good high frequency characteristics, it has been well known to orient the axis of easy magnetization of the anisotropy in a direction perpendicular to the direction of magnetic flux in the magnetic flux path of the magnetic head.
Accordingly, in a magnetic head as shown in FIGS. 1 and 2, when forming a magnetic thin film 12, the direction of the magnetic field is oriented in the a direction of the width W of the head core. In FIGS. 1 and 2, 11 denotes a substrate, 12 is the magnetic thin film made of Fe-Ni alloy, 13 is a gap regulating film, 14 is a coil and 15 is an insulation film.
In case magnetic anisotropy caused by the annealing is strong, a sufficient permeability can not be obtained. Therefore, there is required any kind of process to decrease the magnetic anisotropy.
One known method of decreasing the magnetic anisotropy is to apply a rotation magnetic field onto a magnetic head assembly during the forming of the magnetic thin film on the substrate. However, the apparatus for applying the rotation magnetic field is very complicated and is not suitable for mass-production.
Another method is to make the temperature during formation of the magnetic thin film as high as possible so as to decrease the magnetic anisotropy. In the case when the magnetic thin film is formed of a poly crystalline material, the grain diameter of the crystal becomes larger at the high temperature, thereby resulting in a decrement of the permeability. On the other hand, in case when the magnetic thin film is formed of an amorphous material, the amorphous material is crystallized in the high temperature range, resulting in a decrement of the permeability. Thus the second method is also not sufficient to obtain a good result
In addition, there has been proposed another kind of magnetic head employing head cores made of amorphous magnetic material of the strip type formed by way of the rapid quenching method. In this method, it is difficult to control the magnetic anisotropy at the time of the production of the amorphous magnetic material. Therefore, the magnetic anisotropy is controlled by annealing under the magnetic field at the time immediately after production of the strip type amorphous magnetic material or after the magnetic core is formed. However, since the initial conditions of the amorphous material are different portion by portion of and/or product by product, it is difficult to control the magnetic anisotropy in a uniform manner.